This invention relates to survivability enhancement. It is frequently desirable to enhance the survivability of various structures, including fixed and movable structures, and, depending on particular applications, survivability enhancement structure may be placed on internal or external surfaces, or both of the structure whose survivability it is desired to enhance.
In particular applications, survivability enhancement structures are applied to external surfaces of the vehicle or system. Armored vehicles, for example, are designed to provide ballistic protection commensurate with a specific threat. In connection with such vehicles and systems, the ability to readily vary the ballistic protection configuration or to quickly repair damaged armor as a function of particular threats to which the vehicle or system may be exposed may enhance survivability. Further, arrangements which reduce vehicle "signature" (as a function of electromagnetic radiation, infrared radiation, or the like) may also enhance survivability. The appearance of new vehicle armor in the field stimulates the development of new munitions with enhanced capability to defeat the newly fielded armor. Applique armor, that is, supplemental armor applied on top of the basic armor designed into the vehicle or system, has been proposed to enhance survivability. It has been proposed to attach such applique armor to the basic armor by adhesive bonding, by mechanical bolting and by magnetic attachment.
Other survivability enhancement structures may be placed on internal surfaces of preexisting structures for enhanced ballistic protection or the like. An example of such a survivability enhancement structure is a liner to capture spall, that is material that flies out of the interior surface of a wall structure when a shock wave propagates through the wall. When the compressive shock wave travels through the wall material, it eventually reaches the interior surface (the side furthest from the attack). If the wall material has a free face or is in contact with another material with very different physical properties (e.g. density, sound propagation velocity, etc.) the shock wave will reflect and cause tensile forces to be created which, if they exceed the ultimate strength of the wall material, cause pieces of the wall material to fly off in the direction of travel of the compressive wave. These pieces can travel at high speed and become lethal projectiles in and of themselves. Spall liners (frequently made of high tensile strength fibrous material (aramid (Kevlar), polyethylene (Spectra), Nylon, etc.)) may be of single ply, or quilted into a multi-ply "blanket" and hung in place, much like a curtain, or bolted in place.
In the bolted case, the spall liner is rigidly attached and the mechanism of absorption of the kinetic energy of the flying spall is delamination (inter-laminar shear) and subsequent inter-fiber or fiber-matrix frictional dissipation. If the delamination process fails to occur, and if the kinetic energy is high enough relative to the projected area of the projectiles, "punch-through" will occur and the lethality of the projectile will not be reduced substantially. Similarly, if the rigid spall liner structure is bonded or glued in place, the existing structure to which it is bonded provides reinforcement against deflection, increases the required inter-laminar shear forces necessary for the onset of delamination and consequently reduces the overall ballistic performance of the liner (increases the likelihood of punch-through).